Aerial variable-rate applications proving their worth

Elton Robinson | Apr 28, 2005

HELENA, Ark. — When all the technology came together for variable-rate aerial applications, applicator Paul Riddell was ready to fly with it — well, almost ready.

Riddell, who works for Griffin Ag Inc., a flying service in Helena, Ark., waited until Dan Shannon of Shannon Agricultural Flying, Inc., in Clarksdale, Miss., test-flew the system and gave it a thumbs up. “Once I talked with Dan, who said it worked great, and heard that InTime, Inc. (a precision agriculture provider) was satisfied that the system worked well, I was convinced I needed one.”

Riddell purchased a variable-rate system prior to the 2004 season, spending about $53,000. There are three basic components: a Satloc M3 AirTrac VR Ready GPS, which provides GPS position updates five times per second at a speed of 150 miles per hour; an Auto Cal rate controller and an AG Air Systems hydraulic spray system.

Air Repair, Inc., in Cleveland, Miss., installed the system on Riddell’s AT 802A AirTractor, which has an 800-gallon capacity and a 2.5-ton dry capacity. The rig has a drop boom configuration with 92 CP aerial nozzles. He uses Satloc’s Mapstar software program.

Most of the price of the system, about $32,000, is in the hydraulic spray pump — powered through the plane’s turbine engine drive.

Another important key is the Auto Cal rate controller, produced by Houma Avionics, Houma, La. “AirTrac reads the prescription from the data card and sends that information to the Auto Cal,” Riddell said. “The Auto Cal either speeds up or slows down the hydraulic pump or cuts it completely off for a zero rate.”

Another rate controller, the Del Norte IntelliFlow can also do the job, according to Riddell, although he hasn’t tried the controller himself.

In 2004, Riddell flew variable-rate applications of plant growth regulator, insecticide and defoliant on about 15,000 acres. He charges between $1 and $1.50 for VR services.

Plant growth regulator applications worked extremely well, according to Riddell. “Farm managers said they had never seen fields that even before, and they made the best cotton they ever made. Of course, everybody did last year.

“We had one 240-acre field that was highly variable, with a lot of sand and a rolling elevation. It harvested 47 modules, 11 modules more than it had ever picked before.”

Variable-rate aerial applications of defoliant were also impressive, according to Riddell. “Some fields are going to have really rank areas where you may have to apply a pre-conditioning shot of defoliant. But 80 percent of the variable-rate defoliated fields defoliated perfectly. In seven to 10 days, they were ready to harvest.”

At 150 miles per hour, Riddell’s aircraft covers 222 feet per second. Grid sizes for variable-rate aerial applications are typically 90 feet by 200 feet. The GPS knows its position four to five times within each grid, meaning one update is provided every 44 feet.

Ground rig grids are typically 90 feet by 60 feet.

A 20-hertz Satloc receiver (the current one is 5-hertz) is due out this year, which will provide updates 20 times per second, or every 11 feet. This could shorten the grid length for aerial applications by 30 feet, Riddell said.

A variable-rate injection system is being tested and could also be available in 2005, noted Riddell. “With current technology, when we tank-mix insecticides with Pix for a variable-rate application, we have to overexpend on our insecticide to put out the higher rates of Pix. With injection, we can broadcast the lowest kill rate for the insecticide, and inject the Pix at any rate. The problem with the injection system is finding where to put the batch tank for the injection.”

Dry fertilizer application capability and variable-flow nozzles for aerial variable-rate applications could be available in 2005, too. The pulsating nozzle system will allow for split boom work and narrower grid sizes.

“The system works a lot better if you keep a lot of pressure on the boom, somewhere in the neighborhood of 40 psi. When you get down to 10 psi, it’s sluggish because the pump needs some back pressure.

New high-pressure nozzles from Delavan, which could be on the market this year, are expected to provide up to a 4X rate change at a high-pressure range of “probably between 40 psi and 48 psi,” Riddell said. “Our spray testing indicates that we’re getting less drift with more pressure. The droplet is coming out at a faster speed. At lower pressures, the droplets were coming out slower and were shattering in the air.”

The new nozzles could help out on constant rate applications, too, according to Riddell. “We had to change the orifice size if we wanted to go from 3 gallons to 10 gallons. We won’t have to do that anymore, so we’re not going to have to put our hands on chemicals on the nozzles.”

While cotton has been the primary focus of variable-rate aerial applications up to now, the technology could expand to rice and soybeans.

Riddell said the system is basically maintenance-free. “You have a couple of extra gear drives that you have to maintain lubrication on, and every 100 hours, you change the hydraulic oil filter.”